1. Field of the Invention
This invention relates to hoisting devices. More particularly, this invention relates to a collapsible and portable hoisting device for lifting heavy loads. More particularly still, this invention relates to such a hoisting device configured to be stowed on a small truck, such as a pickup truck, in such a manner that it is available for ready deployment and use in moving a heavy object either onto or off of the truck.
2. Description of Prior Art
Hoisting devices are used to lift and convey objects weighing several hundred to several thousand pounds without the need to use power equipment such as forklifts or mobile cranes. Numerous such devices are used in industrial settings, where they are often used to load and unload trucks. Industrial-sized hoists for such purposes are typically very large and usually permanently installed at hoisting stations dedicated to the requirements of a particular type of truck. They do not provide any help for the occasional need to hoist a heavy object, or even, for the need of the many individuals and businesses that deliver and pick up heavy objects repeatedly at locations not equipped with any type of hoisting or lifting mechanism. For example, individuals and businesses with pickup trucks have periodic need to transport such things as bricks, lumber, logs, large stones, trees with root balls, mechanical systems and office supplies. These and other items routinely need to be delivered to various construction sites and other locations, but not to the extent that would justify the expense of installing a permanent hoisting mechanism at any one of these sites. Thus, and especially for the intermediately heavy loads—those that are very heavy but still capable of being lifted by one or two workers, such as a packet of roofing tiles or bricks for a fireplace the burden of loading and off-loading frequently falls on the arms and backs of the workers. Lifting and conveying of heavy objects by hand is considered to be the single largest source of on-the-job injury in occupations involving manual labor.
Ideally, a hoisting device for handling loads up to one to two thousand pounds would be installed on all the trucks that might be engaged in the type of pickup and delivery described above. Such a device must be capable of being stowed when not in use and readily erectable when needed. Furthermore, it is desirable that the device be such that it can be assembled, operated and disassembled by a single person within a reasonable time interval, say, less than an hour.
Several attempts have been made to provide a portable hoist for use with a pickup truck. For example, Johnson (U.S. Pat. No. 5,862,926) discloses a pickup-truck-loading hoist that can be disassembled for stowing when not needed. When deployed, it consists of a front frame and a rear frame that support a trolley rail running between the frames and extending out behind the rear frame, that is, out beyond the end of a truck bed. Unfortunately, the Johnson hoist disassembles into a large number of individual pieces for which there is no systematic mechanism for securely storing them in or on the truck. This means that the loose pieces must either be carried in the bed of the truck, or removed from the truck, pending the next need for the hoist. There are obvious disadvantages with each option. Moreover, there are other disadvantages with the Johnson hoist. When the pickup's bed is fully loaded, it appears to be difficult to disassemble and store the hoist. Also, deployment of the hoist requires that the pickup's tailgate be removed, the rear frame of the Johnson hoist needing to rest on the trailer hitch. Finally, the nature of the rear frame of the Johnson hoist serves as a serious bottleneck in the degree to which it restricts the size of a load that can be handled by the hoist and transported by the truck, because of the relatively small clearance that it permits between the carrying member and the bed of the truck on which it is installed. In addition, when deployed, the section of the rail extending beyond the back of the truck is not directly supported; it is cantilevered. Thus, the load that a rail of given bearing strength can support is less that it would be if it were supported closer to its end point. For lifting heavier loads, a heavier rail and/or additional frames and braces are required. The use of additional frames or braces, however, results in greater effort to assemble/disassemble the hoist. Or a heavier rail may be safely installed only by the efforts of two or more people, which is a disadvantage.
Sunderland (U.S. Pat. No. 4,930,970) also discloses a portable hoist for use with a pickup truck. The hoist of Sunderland consists principally of a vertical front post and a vertical rear frame that, when the hoist is assembled, support a trolley rail that extends rearward from the back of the truck bed. For disassembly, the post, frame and rail can be collapsed into the truck bed. This presents the same disadvantage as Johnson in that storing the hoist in the truck bed reduces the primary advantage of having a vehicle with a truck bed in the first place-valuable cargo space in the bed is occupied by the hoist.
The Sunderland hoist has other disadvantages. For example, if a load takes up the width of the bed, the hoist cannot rotate down into the bed for travel. In addition, when deployed, the section of the rail extending beyond the back of the truck is not directly supported. Thus, the load that a rail of given bearing strength can support is less than it would be if supported closer to its end point. For lifting heavier loads, a heavier rail and/or additional frames and braces are required. The use of additional frames or braces, however, results in greater effort to assemble/disassemble the hoist. Or a heavier rail may be safely installed only by the efforts of two or more people, which is a disadvantage. Lastly, the outrigger support system disclosed by Sunderland requires that the truck on which the system is to be installed undergo substantial modification. Use of the outriggers is desirable when loading/unloading heavy loads, to relieve stress on the truck's suspension system, but adding them in the Sunderland system is an added inconvenience.
What is needed, therefore, is a collapsible hoist mountable on a truck and easily deployed, operated and stowed by a single person. What is further needed is such a hoist that is capable of lifting an object that is initially several feet beyond the end of the truck and depositing it in the truck's cargo bed, where the object is equal in weight to the load-bearing capacity of the truck. What is yet further needed is such a hoist that occupies minimal space on the cargo bed when the hoist is deployed and minimal space when it is stowed. Finally, what is needed is such a hoist that is easily mounted on and detached from its host truck without the need to modify the truck's frame.